DOC: Removing tailing whitespaces in .rst files

[datapythonista]

• closes #xxxx
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

In #24216 we will start linting formatting errors in .rst files. Removing all the tailing whitespaces here, so we don't mix the cleaning with the code in that PR.

[codecov]

Codecov Report

Merging #24281 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #24281   +/-   ##
=======================================
  Coverage   92.22%   92.22%           
=======================================
  Files         162      162           
  Lines       51828    51828           
=======================================
  Hits        47798    47798           
  Misses       4030     4030

Flag	Coverage Δ
#multiple	90.62% <ø> (ø)	⬆️
#single	43% <ø> (ø)	⬆️

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[codecov]

Codecov Report

Merging #24281 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #24281   +/-   ##
=======================================
  Coverage   92.22%   92.22%           
=======================================
  Files         162      162           
  Lines       51828    51828           
=======================================
  Hits        47798    47798           
  Misses       4030     4030

Flag	Coverage Δ
#multiple	90.62% <ø> (ø)	⬆️
#single	43% <ø> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 040f06f...5d14ce6. Read the comment docs.

[jreback]

thanks!